Disclaimer: I never used Canon and I never tracked high speed objects.

1. AF sensor is an image sensor albeit having low resolution. If you track moving target with camera the background starts moving and gets smudges on the AF sensor therefore making it easier for camera to decide what to focus on.

2. I do not expect larger aperture lens to work better because brightness is far from being the limitation IMO (and because DoF is already too small).

3. AF motor speed depends on how far the target is and (as you pointed out) at which angle it's moving relatively to the eyesight. If a bicycle is riding towards you at constant speed the motor will have to work faster over time. There's very simple test you can do: ask somebody to ride at constant speed towards you and do slow burst of photos. You will then see with your own eyes the limitation of AF motor (the bigger the speed the further away the rider on the last sharp photo will be). I bet it will be significantly harder to find this information online because there's no standard testing methodology for this.

You did not explicitly ask about anything other than AF and your pictures do not have good resolution but IMO you should shorten your exposure (the scarf looks smudged in first example and the print on the shirt looks smudged in the second example even though it's apparently inside sharp field) and close down the aperture (the driver does not even fully fit inside depth of field on second example). This will inevitably increase noise but you need to compromise to get sharp images.